An optical system is used in image duplication devices such as facsimile machines, copiers and printers. In general, the optical system is housed in a single housing unit and is located near an intermediate image-forming surface such as a photoreceptor drum. The optical system includes an image-forming light source, an image-reflecting surface and an image-focusing element to form a desired image on the intermediate image-forming surface by repeatedly scanning the image-forming light in a predetermined direction. To accomplish an efficient scanning, the image-reflecting surface has multiple reflecting surfaces and is rotated at a high speed. The light source is located at a certain distance from the rotatable reflecting surface at a predetermined angle so that a desired scanning angle is obtained. For these and other reasons, the above described prior art optical housing unit generally takes a certain amount of space.
In the efforts to manufacture compact duplication devices, the above described optical system or housing unit needs to be reduced in size. Referring to FIG. 1, one prior art attempt in reducing the overall size of the optical housing unit includes Japanese Patent 5-19196 which discloses an optical housing unit 50 whose mounting portions 51A, 51B and 51C are located inside the optical housing unit 50. Thus, space occupied by otherwise protruding mounting portions 51A-51C is saved, and the overall housing unit size is reduced.
Still referring to FIG. 1, Japanese Patent 5-19196 further discloses a light source 1 located adjacent to a rotatable image-reflecting surface 8 so as to reduce the overall size of the housing unit 50. The light source 1 emits an image-forming light towards the rotating image-reflecting surface 8 which scans the light within a predetermined scanning angle through an image-focusing lens 4. The scanned light is thus focused on a predetermined intermediate image-forming surface by a focusing lens 4 to form a desirable image thereon. However, a certain predetermined distance must be provided between the reflecting surface 8 and the image focusing element 4. Additionally, the relative position of the light source 1 is inflexible with respect to the position of the rotatable reflecting surface 8. In other words, the light source 1 must be placed outside of the scanning angle of the rotatable reflecting surface 8, and a relatively large angle of incidence of the incoming light on the reflecting surface 8 also must be maintained. Consequently, the reflecting surface area needs to be relatively large. For these reasons, the overall housing unit size is not substantially reduced.
Referring to FIG. 2, another prior art effort as disclosed in Japanese Patent 6-148541 employs an additional reflecting surface 60 between a light source 1 and a rotatable reflecting surface 8 for modifying an angle of the originally emitted light by the light source 1. The use of the angle modifying reflecting surface 60 allows the positional arrangement of the light source 1 and the rotatable reflecting surface 8 to be more flexible. However, the above described large angle of incidence as well as a large reflecting surface area on the rotatable reflecting surface must be still provided to form a desirable image.
In view of the above prior art, a flexible compact optical system is desired for various duplication devices of a further reduced size.